There are beautiful festivals in South Korea.
One of them is Lotus Lantern Festival. We can see this festival at the heart of Seoul. In other worlds, you can see this festival at Cheonggyeocheon stream. It falls on normally May 15 or before and after some days.
Please check the beautiful scenery at Cheonggyeocheon stream, when you visit Seoul. You can see these Lotus Lantern Festival all across the country. Don't be disappointed if you are out of Seoul. There are many Buddhist temples where you can see Lotus Lanterns, for example Bulkuksa temple, Seokguram grotto in Gyeongju etc.
This festival originated from Silla dynasty(BC57 ~ AD935), and became very popular during Goryo dynasty (AD918 ~ AD1392). It is very popular still in Korea. in case of May 16, 2015 300,000 people participated in the parade of Lotus Lantern festival.